Method for etching a trench having rounded top corners in a silicon substrate

Abstract

The present disclosure includes a method of plasma etching a trench having rounded top corners in a silicon substrate. One embodiment includes the following general steps: a) providing a semiconductor structure comprising a hard masking layer, overlying a silicon substrate; b) plasma etching through said hard masking layer and any additional underlying layers overlying said silicon substrate using at least one plasma feed gas which does not provide polymer deposition on surfaces of said semiconductor structure during etching; where said plasma etching exposes a face of said silicon substrate; and c) plasma etching at least a first portion of a trench into said silicon substrate using reactive species generated from a feed gas comprising a source of fluorine, a source of carbon, a source of hydrogen, and a source of high energy species which provide physical bombardment of said silicon substrate. Top corner rounding is effected by deposition of a thin layer of polymer on a top corner of the trench during etching of the first portion of the trench, resulting in the formation of a rounded "shoulder" at the top corner of the trench. Typically a layer of silicon oxide overlies at least a portion of the silicon substrate surface. The method described provides excellent critical dimension control over the active area of a transistor produced using the method and reduces the need to remove polymer from substrate and reactor surfaces after etching of the silicon trench.

Description

1. Field of the InventionThe present invention pertains to a method for etching a trench in a silicon substrate. In particular, the present invention pertains to particular plasma etch chemistries, process conditions, and a series of steps which may be used to produce rounded top corners on a trench etched in a silicon substrate. The term "top trench corner" refers to the transition from the upper sidewall of a trench to the upper surface of the substrate in which the trench is formed.2. Brief Description of the Background ArtTrenches formed in silicon using traditional etching methods typically have sharp, squared-off top corners. These sharp, squared-off corners lead to high field stress in film layers subsequently deposited thereon during further processing steps. The high field stress can potentially lead to the electrical breakdown of the overlying deposited film layers. Further, the sharp, squared-off corners are a point of charge accumulation, which can cause edge leakage. Ro...

AI Technical Summary

Problems solved by technology

These sharp, squared-off corners lead to high field stress in film layers subsequently deposited thereon during further processing steps.

The high field stress can potentially lead to the electrical breakdown of the overlying deposited film layers.

Further, the sharp, squared-off corners are a point of charge accumulation, which can cause edge leakage.

However, rounding of the corners in a manner which results in a loss of device active area is undesirable.

A sharp corner at the bottom of a trench can also be a source of stress, causing problems of the kind described with reference to the top corners of the trench.

Subsequent to the break-through step, a

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